1. Field of the Invention
This invention relates to an apparatus for starting a teaching-playback robot, and more particularly to an apparatus for starting a playback action of the robot when a workpiece on a conveyer is transferred to an optimum position for the robot operation.
2. Description of the Prior Art
Illustrated in FIG. 6 is an example of a conventional starting apparatus for teaching-playback robots. The conventional apparatus which is generally indicated at 11 employs a plurality of start signal generating means 14, 15 and 16 at positions located beside a conveyor 12 carrying workpieces W1, W2 and W3 and upstream of a teaching-playback robot 13, counting the number of conveyer pulses which are generated by a conveyer pulse generator 18 in synchronism with the movement of the conveyer 12 upon detection of a workpiece by one of the start signal generating means to start playback action of a working program by the teaching-playback robot 13 as soon as the number of the conveyer pulses reaches a predetermined number.
A plurality of start signal generating means 14 to 16 are provided to cope with the different kinds of workpieces W1 to W3. The start of playback action is delayed by counting a predetermined number of the conveyer pulses until the workpiece is transferred a distance D and advanced to a position in front of the teaching-playback robot.
Namely, as shown particularly in FIG. 7(a), the start signal generating means 14 is selected for the workpiece W1, and the playback action of the teaching-playback robot 13 is started at a point in time when the workpiece W1 has been transferred a distance D after detection by the start signal generating means 14. The operation is started when a working part of the workpiece W1, for example, the front side portion of the workpiece W1 reaches a position in front of the robot 13 to let the teaching-playback robot 13 operate in an optimum working range. For the workpiece W2, the start signal generating means 15 is selected as shown in FIG. 7(b). Accordingly, the playback action of the working program is started when a working portion of the workpiece W2, for example, the upper side portion of the workpiece W2 reaches to a position in front of the teaching-playback robot 13. Further, as shown in FIG. 7(c), the start signal generating means 16 is selected for the workpiece W3. In this case, the playback action by the robot 13 is started when a working portion of the workpiece W3, for example, the rear side portion of the workpiece W3 reaches to a position in front of the robot 13.
Accordingly, it has been necessary to provide a plurality of start signal generating means respectively for a plurality of workpieces W1 to W3 of different types to let the teaching-playback robot 13 operate constantly in an optimum working range.
However, the above-described conventional apparatus which needs to provide a large number of start signal generating means depending upon the kinds of workpieces is complicated in structure and very costly, coupled with a problem in that the actual number of start signal generating means has a limit and cannot be increased more to cope with a great diversity of workpieces.